The majority of “Transformers: Dark of the Moon” is an incoherent mess. Plot strands and characters (both human and robotic) are dangled on the screen for 90+ minutes, only to come together for a propulsive hourlong battle.

The last hour, powered with excellent 3D special effects, is undeniably spectacular. Your patience for nonsense will be the ultimate decider in choosing to sit through the entirety of director Michael Bay’s brain-numbing adventure.

Shia LaBeouf headlines again as Sam Witwicky, now a college grad and on the hunt for a good job. The government won’t allow him to place “two-time world saver” on his resume, and the national security director (Frances McDormand) has blocked him from working alongside the Autobots on their latest bout with the evil Decepticons.

Don’t get excited about cool robot battles just yet. Too much of “Dark of the Moon” focuses on Sam’s personal antics, and there’s another insufferable appearance by his parents (played by Julie White and Kevin Dunn). His new girlfriend (Victoria Secret model Rosie Huntington-Whiteley) also serves no purpose other than looking nice walking/running/blinking in slow motion.

The robot storyline involves the discovery of a massive ship hidden on the dark side of the moon. Autobot leader Optimus Prime reboots the ship’s pilot, Sentinel Prime, who reveals a Decepticon plot to invade Earth and enslave the human race. The metal clanging really gets going when the bad guys select Chicago as their first invasion locale.

There’s a bunch of hooey involving series returnees John Turturro, Tyrese Gibson and Josh Duhamel, and newbies John Malkovich and Patrick Dempsey have odd supporting roles, but none of it really matters. Plot strands are left dangling, the movie jumps randomly between set pieces, and Bay fills in the script holes with banal speeches about freedom and vanquishing evil. Beautifully photographed American flags can be spotted every few minutes.

This would all be fine if “Dark of the Moon” clocked in at a reasonable running length. Everything here is bloated, and even the final battle gets repetitive after the first dozen or so robot showdowns. And why does Optimus Prime, the robot with the best combat skills, always miss out on the majority of action? He can take down five Decepticons in a single move, but a few dangling construction wires keep him busy for most of the fight.

“Dark of the Moon” is unquestionably better than the last film, “Revenge of the Fallen,” a movie so bad even Bay admitted as much in recent interviews. Still, this new movie lacks the attention to character that was (somewhat) present in the first film. Other than Optimus and Sam’s heroic yellow protector, Bumblebee, the robots are basically only identifiable by color.

At least the 3D in “Dark of the Moon” utilizes the format to its maximum potential. Bay has thankfully slowed some of his furious camerawork to make the action fill the added dimension without overworking the senses.

The action is cool, but the rest of the movie generally stinks. Why does it feel like I’ve done nothing to sway you?

Grade: C